Exhaust valve color

[checksix]

Hi Guys,

I had to remove the exhaust manifold today on my 1974 18RG that is stuffed into an Austin Healey Bugeye Sprite, and when looking around, I noted the #3 valve was white, while the other 3 ports were a sooty black. My 1st thought was a lean mixture, probably dirt somewhere in the carb. I should note that I've been swapping jet combinations quite frequently while I was tuning it using an O2 sensor. To try and understand this better, I pulled 2 spark plugs so I could relate the differences seen on the valve. I pulled #3 (the white valve), and #4 (which looks identical to number's 1 & 2 with a sooty dark look. You'll have to see the pictures to believe, as both spark plugs look scary similar. I'll admit this is a bit past my experience. The carb is a Solox ADDHE, and all 4 are set up identical down to the screw settings for idle mix. So what's going on here? With everything identical, why is #3 different?

Sorry, I can not get the pictures to load, never a problem in the past, but who knows. I'll try in the future.

Checksix

[davew7]

Possible coolant leak i.e. head gasket. Is the coolant level low or is oily. If you have a compression tester, I would do a quick check. Davew7

[checksix]

Possible coolant leak i.e. head gasket. Is the coolant level low or is oily. If you have a compression tester, I would do a quick check. Davew7

I remember some time ago a similar look on a different engine and it was antifreeze. I checked my antifreeze and it might be down slightly, but really hard to tell. There is no blow back into the cooling system, and no oily indication at all. I have yet to do a compression check, but I believe it would be okay as this leak is really small, if it is antifreeze as suspected.

Any other members who might have an opinion as to the cause? I'm on the fence about doing a head gasket as it is quite a lot of work, but if it is the beginning of a leak, it's not likely to get better. I'd just like some better confidence before making such a big step. If I do do a gasket change, how much material can I remove from the head to get an even surface? Is there a way to measure my head to see if it had been decked prior, and what it the limit of removal?

Checksix

[davew7]

If the antifreeze is only slightly down and it's not an oily mess, I would just try one of the stop-leak products. It's worth a try. I suggest using a stop leak, that chemically re-acts, when exposed to combustion gases Vs the type that plugs the void.

Davew7

[checksix]

If the antifreeze is only slightly down and it's not an oily mess, I would just try one of the stop-leak products. It's worth a try. I suggest using a stop leak, that chemically re-acts, when exposed to combustion gases Vs the type that plugs the void.

Davew7

I have never heard of the type that reacts to the combustion gasses. Can you suggest one? I'll try to do some research tonight on it as well. Still sitting on the take it apart fence.

[jondee86]

For a small leak I would suggest you try this stuff... check it out before you
decide what to use. As you suggest, a lot of the widely advertised stop leak products
are liable to do more harm than good.



Cheers... jondee86

[checksix]

For a small leak I would suggest you try this stuff... check it out before you
decide what to use. As you suggest, a lot of the widely advertised stop leak products
are liable to do more harm than good.



Cheers... jondee86

This was always my go to product in previous problems. My research tonight brought up several products that were supposed to be heat activated. The reviews were really mixed with 10% or more writing negative reviews, mostly complaining that the product stopped up heaters and radiators. I'm leaning more towards fixing it with a gasket replacement but would love to hear actual success / failure stories.

Can a head be measured to tell how much I can remove to get it flat? I wouldn't mind raising the compression some, so what is the minimum head thickness?

[jondee86]

Can a head be measured to tell how much I can remove to get it flat? I wouldn't
mind raising the compression some, so what is the minimum head thickness?

Can't help with how thick the head might have been when new. But generally speaking
I would get the machine shop to check the head for flatness and only take off the minimum
required to get it flat and remove any pitting.

From memory, I think you should be looking for around 0.8mm squish so you will need to
measure the deck height when the head is off and go from there. Better to use a thinner
head gasket than to take a lot off the head. Just my 2c

Cheers... jondee86

[davew7]

An un-cut head will be 116mm (4.566") tall. Ideal squish for a 4AGE is .032 to .038". Every .004" removed from the head surface is about a .5cc volume reduction. A .010" cut is equal to a 1.28cc reduction. I have actually machine the 4AGE head down to within a few thousands of the valve seat. If you want to look at thinner head gaskets I can highly recommend the Cometic MLS gaskets. You should consider adjustable cam gears if you remove more the just a clean up cut on the head. Davew7

[73GTV]

Can't help with how thick the head might have been when new. But generally speaking
I would get the machine shop to check the head for flatness and only take off the minimum
required to get it flat and remove any pitting.

From memory, I think you should be looking for around 0.8mm squish so you will need to
measure the deck height when the head is off and go from there. Better to use a thinner
head gasket than to take a lot off the head. Just my 2c

Cheers... jondee86

He speaks the truth....

Do the compression test. Confirm the health of the Block and the sealing of the head first.